A hybrid automatic repeat request (HARQ) is a technology formed by combining forward error correction (FEC) code and an automatic repeat request (Automatic Repeat Request, ARQ). In a Long Term Evolution (LTE) system, to support an HARQ, a terminal needs to feed back an HARQ-acknowledgment (HARQ-ACK) to a base station by using a physical uplink control channel (PUCCH) and a physical uplink shared channel, PUSCH). The HARQ-ACK includes an acknowledgment (ACK) and a negative acknowledgment (NACK).
An existing LTE system includes two types of radio frame structures. A frame structure type 1 is applied to frequency division duplex (FDD), and a frame structure type 2 is applied to time division duplex (TDD). The frame structure type 1 is shown in FIG. 1, and the frame structure type 2 is shown in FIG. 2. FIG. 1 is a schematic structural diagram of a frame structure type 1 in an existing LTE system. FIG. 2 is a schematic structural diagram of a frame structure type 2 in an existing LTE system. In the frame structure type 2 shown in FIG. 2, DwPTS is a downlink pilot timeslot (DwPTS), UpPTS is an uplink pilot timeslot (UpPTS), and GP is a guard period (GP). For both the frame structure type 1 and the frame structure type 2, each radio frame includes 10 subframes, and a length of each subframe (Subframe) is 1 millisecond (ms). For the TDD, seven types of uplink-downlink configurations exist in the existing LTE system, as shown in Table 1.
In Table 1, D is a downlink subframe, U is an uplink subframe, and S is a special subframe.
In the existing LTE system, for the FDD, an HARQ-ACK corresponding to a physical downlink shared channel (PDSCH) transmitted in a downlink subframe n-4 is fed back in an uplink subframe n. For the TDD, an HARQ-ACK corresponding to a PDSCH transmitted in a downlink subframe n-k is fed back in an uplink subframe n, where k belongs to a set K. In a case of all TDD uplink-downlink configurations, a set corresponding to K is shown in Table 2.
TABLE 1Downlink-to-uplink Uplink-downlinkswitch-point Subframe numberconfigurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
TABLE 2Uplink-downlinkSubframe numberconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 6, 5, ——————7, 114, 75——13, 12, 9, ———————8, 7, 5, 4, 11, 66——775——77—
In an evolved LTE system in the future, to reduce a service delay, a length of each subframe is shortened, for example, a length of each subframe is shortened to 0.2 ms, and a new subframe type 1 and a new subframe type 2 are introduced. For example, FIG. 3 is a schematic structural diagram of a new subframe type 1 in which a length of each subframe is 0.2 ms. FIG. 4 is a schematic structural diagram of a new subframe type 2 in which a length of each subframe is 0.2 ms. A subframe that is shortened in terms of time may be referred to as a short subframe or an ultra-short subframe, or may be referred to as a short transmission time interval (TTI) or an ultra-short TTI. When a length of the short subframe is 0.2 ms, a short subframe may include 11 symbols (which may be single carrier frequency division multiple access (SC-FDMA) symbols) in a time domain. For example, as shown in FIG. 3, for the new subframe type 1, the first nine symbols are used for downlink transmission, one symbol is used for a guard period (GP), and one symbol is used for uplink transmission. For example, as shown in FIG. 4, for the new subframe type 2, the first symbol is used for downlink transmission, one symbol is used for a GP, and the remaining nine symbols are used for uplink transmission.
When a frame structure based on a short subframe is used, how to feed back an HARQ-ACK needs to be designed again, so that when a new subframe structure is used, a system can provide a service having a low service delay requirement, and large enough coverage of the new subframe structure can be ensured.